1. Field of the Invention
The present invention relates generally to a flat display such as liquid crystal display (LCD), plasma display panels and applied devices thereof. More particularly, the present invention relates to a flat display device having such a configuration that a display body module and a display control unit for controlling the display are separately disposed, as well as to a display body driving device.
2. Background Technical Art
A portable personal computer and word processor known as a so-called laptop type generally have hitherto incorporated an opening/closing type flat display unit. Middle-and-large-sized liquid crystal display devices mounted therein each consist of, as illustrated in FIG. 9, a liquid crystal display unit 10 built into the device body and a flat liquid crystal display module unit 20 provided inwardly of an opening/closing cover so that these units are separately independently disposed. The liquid crystal display control unit 10 includes a liquid crystal module controller 12 and a microprocessor unit (MPU), not shown. The liquid crystal module controller 12 supplies a variety of control signals and clock signals to liquid crystal display module unit 20. The liquid crystal display module unit 20 has: e.g., a simple matrix type liquid crystal display panel (matrix liquid crystal display elements) 22; a signal electrode driving circuit (X drivers) 24 and a scan electrode driving circuit (Y drivers) 26 which are TAB-packaged in peripheral regions (frame) of the panel 22; and a liquid crystal power source circuit 28 for generating high liquid crystal driving voltages (reference voltages) V.sub.0 -V.sub.5. Signal electrode driving circuit 24 is composed of a plurality of signal electrode driver semiconductor integrated circuits 24.sub.1 -24.sub.m which are cascade-connected. Signal electrode driving circuit 24 supplies driver outputs per picture line to, e.g., M-pieces of signal electrodes in total. More specifically, data signals D0-D7 are sequentially taken in a shift register within the signal electrode driving circuit 24 by pixel clocks (shift clock pulses) XSCL. When the signals (M bits) per picture line are taken in, the data signals within the shift register are transmitted in parallel to a data latch circuit by scan line synchronous signals (data signal latch clocks LP) YSCL. The data signals undergo series/parallel conversion. The data latch circuit holds a signal voltage per line during a 1-scan period. Based on this signal voltage, a selection switch circuit sets output voltages of drivers connected to the signal electrodes either in a selection state or in a non-selection state. The AC-transforming clock FR is a clock for transforming each voltage described above into an AC waveform in order to prevent a deterioration of the liquid crystal elements due to a DC drive. A forced blank display signal DF is conceived as a signal for forcibly placing a liquid crystal picture into a blank display state. The scan electrode driving circuit 26 consists of a plurality of scan electrode driver semiconductor integrated circuits 26.sub.1 -26.sub.n which are cascade-connected. The circuit 26 works to give a section voltage to only one of a total of N pieces of scan electrodes and non-selection voltages to the rest of them, i.e., (N-1) pieces of scan electrodes. A 1-scan line period is started by the scan start pulse (frame start signal) SP. Every time a scan line synchronous signal YSCL (data signal latch clock LP) is present, the selection voltages are sequentially impressed on the scan electrodes from the first line electrode to the N-th line electrode (line sequence display). The liquid crystal power source circuit 28 disposed on the side of the liquid crystal display module unit 20 generates a plurality of liquid crystal driving voltages V.sub.0 -V.sub.5 selected by the selection switch of the scan electrode driving circuit 26 and the signal electrode driving circuit 24. The liquid crystal power source circuit 28 is set in power on/off states by the forced blank display signal DF.
The liquid crystal display control unit 10 built in the device body is connected to the flat liquid crystal display module unit 20 typically through a hinge-connected movable part by using a flexible cable 30. With this arrangement, the cable 30 itself is bent every time the opening/closing cover on the side of the flat liquid crystal display module unit 20 is opened and closed. Signal lines of the cable 30 tend to be damaged or disconnected due to physical factors. If a part of the signal lines are disconnected, there arises a situation where no AC drive is effected in such a state that a DC voltage (DC component) remains impressed on, e.g., a liquid crystal display panel 22. This may result in the deterioration of the liquid crystal display panel 22 which is more expensive than other parts and therefore difficult to repair. This liquid crystal deterioration is conceived as a factor of obstacle to display quality and life span and is a serious problem to the display device based on visual recognizability. Among the signals supplied to the liquid crystal display module unit 20 from the liquid crystal module controller 12, the signals which may induce a decline of the DC drive of the liquid crystal display panel 22 are a scan start pulse SP, a scan line synchronous signal YSCL (data signal latch clock LP), an AC-transforming clock FR, and a logic-side power source voltage Vcc. When some operational abnormalities occur in the liquid crystal module controller 12 and the microprocessor unit (MPU), abnormalities arise in the respective signals. There exists a possibility where the situation similar to the above-mentioned may take place.
Expanding the problem about the DC drive of the liquid crystal display body, this can be generalized to a problem associated with a signal abnormality on the side of the liquid crystal module unit. Besides, where a wall-mounted TV is presumed, because of a display control unit and a display panel being disposed in remote places, a problem in terms of deterioration in display quality is produced due to attenuation of signal level and the influence of noise as well as signal stoppage. As used herein, the term signal stoppage includes abnormal signals, such those signals between the display control unit and the display panel which have been interrupted. Furthermore, problems also occur not only in liquid crystal displays but also plasma displays.
Accordingly, it is an object of the present invention devised in light of the above-described problems to provide a flat display device and a display body driving device which are capable of preventing deterioration of display characteristics due to a DC drive of a display panel, this deterioration being derived from an abnormality of a signal supplied from a display control unit to a display body module unit.